private void btnLogin_Click(object sender, EventArgs e)
        {
            Login nd = new Login(txbName.Text, txbPassword.Text);

            try
            {
                string name = txbName.Text.Trim();
                string pw   = txbPassword.Text.Trim();
                if (nd.kiemTraDangNhap(name, pw) == 1)
                {
                    MessageBox.Show("Login sucessed", "Thông báo", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    Client.Connected += Client_Connected;
                    Client.Connect(); // connect port 2014
                    Client.Send("Connect|" + txbName.Text + "|connected");
                }
                else
                {
                    MessageBox.Show("Error", "Thông báo", MessageBoxButtons.OK, MessageBoxIcon.Information);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }